Opponent lost 100 points in rating in one game vs me.

Generally you and your opponent will win/lose the same amount of points. More if the rating difference is high. We were almost the same rating (700s), so I won 8 points for a checkmate, but my opponent lost almost 100 points for losing!

I wonder what they did to deserve such a penalty.

Do you have a copy of the game? I could look but I agree this is confusing

https://support.chess.com/article/210-how-do-ratings-work-on-chess-com

maybe they were a new player that didnt have a rating yet. when that happens you can lose a lot of rating when losing

But if they were at a 700 rating they already must have played quite a few games to determine a rating

This was a relatively new player, so chess.com has an alg for number of games played vs number of points gained/lost. to help a player find their rating niche. Does that help?

Your opponent had joined chess.com on August 6, 2023 and is in a 300ish rating rn. And before your game they had only played 2 rapid games which ended in a draw. People lose many points in their earlier games as it helps them get to their "real" rating fast. If you want me to explain how that works, it would take a whole another post.

Why did i lose more than 150 points after Losing a match, i am not new here, please help or any reason

You have only had 2 rated rapid games so your rating deviation (RD) value is high and rating changes will be higher and will start dropping as you play more rated games.

Thanks for the Information Martin

It happened to me too twice in a row with my opponent losing 124 points!